The influence of soil surface gradient on rainfall infiltration and related surface runoff generation are not well understood for representation in hydrologic modeling because of conflicting theoretical formulations and experimental results available in the scientific literature. The main objective of this study is to integrate and extend previous laboratory experiments using artificial rainfall over a laboratory setup with adjustable slope angle (α) and consisting of two adjacent natural bare soils that according to the USDA soil classification were of loam (Soil 1) and sandy loam (Soil 2) type, respectively. Soil 2, placed downstream, was subjected to the run-on process due to the overland flow produced over Soil 1. The slope effects are discussed on the basis of measurements of runoff surface (QS) and deep flow (Qd), both strictly linked to the infiltration rate, supported by a simplified rainfall-runoff model. Our results indicate that at a time close to the end of rainfall period (tre=8 h), for α increasing from 1◦ to 10◦, Qd decreased by about 25% while QS exhibited a corresponding increase in magnitude. In the same slope range, at t → tre the total volume of water collected as deep flow decreased by about 40% for heavy rainfall and up to about 50% for light rainfall. On the other hand, a growth of the total surface water volume occurred such that the total outflow volume was nearly independent of α. The run-on effect is seen to modulate the differences in steady deep flows for different slopes. The above variations became of minor interest between 10◦ and 15◦. The significant differences in the variations of surface and deep flow to changes of slope angle were analyzed and placed in context with those from earlier experiments. The differences are attributed to a different level of interaction between capillary and gravitational effects that should be represented in existing infiltration models, because appreciable values of α characterize most watershed areas and the decrease of infiltration with increasing α over bare soils can imply a greater contribution to the direct runoff and a significant reduction of the groundwater recharge with respect to a flat surface.

Experimental evidence for modulation of slope effect on heterogeneous infiltrating surfaces by run-on

Flammini, A.
;
Dari, J.;Saltalippi, C.;Morbidelli, R.;Corradini, C.;
2022

Abstract

The influence of soil surface gradient on rainfall infiltration and related surface runoff generation are not well understood for representation in hydrologic modeling because of conflicting theoretical formulations and experimental results available in the scientific literature. The main objective of this study is to integrate and extend previous laboratory experiments using artificial rainfall over a laboratory setup with adjustable slope angle (α) and consisting of two adjacent natural bare soils that according to the USDA soil classification were of loam (Soil 1) and sandy loam (Soil 2) type, respectively. Soil 2, placed downstream, was subjected to the run-on process due to the overland flow produced over Soil 1. The slope effects are discussed on the basis of measurements of runoff surface (QS) and deep flow (Qd), both strictly linked to the infiltration rate, supported by a simplified rainfall-runoff model. Our results indicate that at a time close to the end of rainfall period (tre=8 h), for α increasing from 1◦ to 10◦, Qd decreased by about 25% while QS exhibited a corresponding increase in magnitude. In the same slope range, at t → tre the total volume of water collected as deep flow decreased by about 40% for heavy rainfall and up to about 50% for light rainfall. On the other hand, a growth of the total surface water volume occurred such that the total outflow volume was nearly independent of α. The run-on effect is seen to modulate the differences in steady deep flows for different slopes. The above variations became of minor interest between 10◦ and 15◦. The significant differences in the variations of surface and deep flow to changes of slope angle were analyzed and placed in context with those from earlier experiments. The differences are attributed to a different level of interaction between capillary and gravitational effects that should be represented in existing infiltration models, because appreciable values of α characterize most watershed areas and the decrease of infiltration with increasing α over bare soils can imply a greater contribution to the direct runoff and a significant reduction of the groundwater recharge with respect to a flat surface.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11391/1532573
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